Evaluation of Attention-deficit/Hyperactivity Disorder in Referred Patients to the PKU Clinic in Yazd, Iran.

Objective: The imbalance of phenylalanine (PA) to tyrosine level and decreased dopamine brain level in patients with phenylketonuria (PKU) may have a role in their susceptibility of them to attention-deficit/hyperactivity disorder (ADHD). This study aimed to evaluate the frequency of ADHD in referred patients to PKU Clinic in Yazd, Iran.

Materials & methods: In this cross-sectional analytical study, all patients older than three years with PKU who were referred to the PKU Clinic of Shahid Sadoughi Hospital, Yazd, Iran, in 2018 were evaluated, and ADHD symptoms in them were assessed via parent face-to-face interview. The patients were diagnosed with ADHD if they scored at least of 20 on ADHD diagnostic rating scale via parent interview based on DSM-VI criteria.

Results: Fourteen boys and 21girls with a mean age of 9.55±1.8 years were evaluated. 51.5% of those diagnosed with PKU had ADHD. Accordingly, ADHD was more frequent in girls (77.8% vs. 41% in boys, P=0.03). The mean age of diagnosis of PKU was significantly higher in patients with ADHD (52.54±15.65 months vs. 29.75±9.65 months, P = 0.03). The mean of PA level in the last six months (15.59±5.95 vs. 8.72+5.18, P= 0.005) and mean of the last six PA levels (14.76±4.71 vs. 8.96±3.86, P= 0.03) were significantly higher in ADHD group.

Conclusion: The prevalence of ADHD in phenylketonuria patients in the present study was much more than in other studies. Late diagnosis of PKU and long-term high PA blood and brain level might be associated with increased neonatal screening. Hence, regular follow-up and continuous evaluation of patients with PKU for ADHD symptoms should be performed.